Tap changers have been in worldwide use in large numbers for many years for uninterrupted switching between different winding taps of tapped transformers. Such tap changers usually consist of a selector for power-free selection of the winding tap of the tapped transformer which is to be switched to and a load changeover switch for the actual switching from the connected to the new, preselected winding tap. The abrupt switching is usually carried out with the assistance of a force storing unit, on the triggering of which a switching shaft is rapidly rotated. The load changeover switch in addition usually comprises switch contacts and resistance contacts. The switch contacts in that case serve for direct connection of the winding tap with the load shunt and the resistance contacts for temporary connection, i.e. bridging-over by means of one or more switch-over resistances.
Such a load changeover switch of a tap changer, which uses vacuum-switching tubes for uninterrupted switching, is known from DE 195 10 809 [U.S. Pat. No. 5,834,717]. In that case, a respective cam disk is provided for each switching element to be actuated and each movement direction of the drive shaft. The edges of the individual cam disks each have a defined profile which departs from a circular shape and by means of which on rotation of the switching shaft individual vacuum-switching tubes or also mechanical contacts are actuated.
In DE 42 31 353 the actuation of the individual vacuum-switching tubes takes place through a switching shaft which is rotatable in both directions and which is rapidly rotated after triggering of a force storage unit. In that case, fixedly arranged on the switching shaft for actuation of the vacuum-switching tubes is a cam disk which has at its edge for each vacuum-switching tube a respective cam formation against which a respective roller, which acts on the actuating lever of the associated vacuum-switching tube, is mechanically urged. The cam formation is here realized in the form of a horizontal annular groove which departs from the circular profile and in which the respective roller mechanically positively engages.
In addition, a load changeover switch operating in accordance with the reactor principle is known from DE 40 11 019 C1, in which the cam disk for actuation of the contacts does not have a profile departing at the annular edge from a circular shape, but possesses on the upper side and lower side thereof grooves with geometrically different shape. A double-sided actuation of different switching elements with a different switching sequence is possible with this known solution.
A disadvantage of these known solutions is the large space requirement of the plurality of cam disks, since a respective separate cam disk is needed for actuation of each individual vacuum-switching tube. This problem is particularly relevant when for realization of the switching sequence a larger number of vacuum-switching tubes per phase is incorporated in the load changeover switch. The available installation space within the load changeover switch is often then no longer sufficient in the known solutions and constructionally disadvantageous compromise solutions have to be adopted.